[compiler] Unnecessary cast warning is not detected when casting a bound

generic type to its super type

fixes eclipse-jdt#2470

org.eclipse.jdt.core.compiler.batch/src/org/eclipse/jdt/internal/compiler/ast/MessageSend.java

@@ -807,25 +807,14 @@ public TypeBinding resolveType(BlockScope scope) {
 	if (this.constant != Constant.NotAConstant) {
 		this.constant = Constant.NotAConstant;
 		long sourceLevel = scope.compilerOptions().sourceLevel;
-		boolean receiverCast = false;
 		if (this.receiver instanceof CastExpression) {
 			this.receiver.bits |= ASTNode.DisableUnnecessaryCastCheck; // will check later on
-			receiverCast = true;
 		}
 		this.actualReceiverType = this.receiver.resolveType(scope);
 		if (this.actualReceiverType instanceof InferenceVariable) {
 				return null; // not yet ready for resolving
 		}
 		this.receiverIsType = this.receiver.isType();
-		if (receiverCast && this.actualReceiverType != null) {
-			// due to change of declaring class with receiver type, only identity cast should be notified
-			TypeBinding resolvedType2 = ((CastExpression)this.receiver).expression.resolvedType;
-			if (TypeBinding.equalsEquals(resolvedType2, this.actualReceiverType)) {
-				if (!scope.environment().usesNullTypeAnnotations() || !NullAnnotationMatching.analyse(this.actualReceiverType, resolvedType2, -1).isAnyMismatch()) {
-					scope.problemReporter().unnecessaryCast((CastExpression) this.receiver);
-				}
-			}
-		}
 		// resolve type arguments (for generic constructor call)
 		if (this.typeArguments != null) {
 			int length = this.typeArguments.length;
@@ -977,6 +966,18 @@ public TypeBinding resolveType(BlockScope scope) {
 		return null;
 	}
 
+	if (this.receiver instanceof CastExpression) {
+		// this check was suppressed while resolving receiver, check now based on this.binding.declaringClass
+		TypeBinding uncastedReceiverType = ((CastExpression)this.receiver).expression.resolvedType;
+		if (uncastedReceiverType == null) {
+			assert this.outerInferenceContext != null : "null should only happen when nested in unfinished type inference"; //$NON-NLS-1$
+		} else if (uncastedReceiverType.isCompatibleWith(this.binding.declaringClass)) {
+			if (!scope.environment().usesNullTypeAnnotations() || !NullAnnotationMatching.analyse(this.actualReceiverType, uncastedReceiverType, -1).isAnyMismatch()) {
+				scope.problemReporter().unnecessaryCast((CastExpression) this.receiver);
+			}
+		}
+	}
+
 	if (compilerOptions.isAnnotationBasedNullAnalysisEnabled) {
 		ImplicitNullAnnotationVerifier.ensureNullnessIsKnown(this.binding, scope);
 		if (compilerOptions.sourceLevel >= ClassFileConstants.JDK1_8) {

org.eclipse.jdt.core.tests.compiler/src/org/eclipse/jdt/core/tests/compiler/regression/AmbiguousMethodTest.java

@@ -2448,7 +2448,12 @@ public void test041() {
 			"}"
 		},
 		"----------\n" +
-		"1. ERROR in X.java (at line 9)\n" +
+		"1. WARNING in X.java (at line 9)\n" +
+		"	String s = ((I) this).foo(0.0f);\n" +
+		"	           ^^^^^^^^^^\n" +
+		"Unnecessary cast from X to I\n" +
+		"----------\n" +
+		"2. ERROR in X.java (at line 9)\n" +
 		"	String s = ((I) this).foo(0.0f);\n" +
 		"	           ^^^^^^^^^^^^^^^^^^^^\n" +
 		"Type mismatch: cannot convert from Object to String\n" +

org.eclipse.jdt.core.tests.compiler/src/org/eclipse/jdt/core/tests/compiler/regression/CastTest.java

@@ -3649,6 +3649,51 @@ public void testBug572534() {
 	}
 }
 
+public void testGH2470() {
+	if (this.complianceLevel < ClassFileConstants.JDK1_6) return;
+	Runner runner = new Runner();
+	runner.testFiles = new String[] {
+			"UnnecessaryCasts.java",
+			"""
+			public class UnnecessaryCasts<T extends C> {
+				void m(T t) {
+					C c = t;
+
+					((C) t).x();
+					((I) t).x();
+					((I) c).x();
+				}
+			}
+
+			interface I {
+				void x();
+			}
+			class C implements I {
+				@Override
+				public void x() {}
+			}
+			"""
+		};
+	runner.expectedCompilerLog =
+			"----------\n" +
+			"1. WARNING in UnnecessaryCasts.java (at line 5)\n" +
+			"	((C) t).x();\n" +
+			"	^^^^^^^\n" +
+			"Unnecessary cast from T to C\n" +
+			"----------\n" +
+			"2. WARNING in UnnecessaryCasts.java (at line 6)\n" +
+			"	((I) t).x();\n" +
+			"	^^^^^^^\n" +
+			"Unnecessary cast from T to I\n" +
+			"----------\n" +
+			"3. WARNING in UnnecessaryCasts.java (at line 7)\n" +
+			"	((I) c).x();\n" +
+			"	^^^^^^^\n" +
+			"Unnecessary cast from C to I\n" +
+			"----------\n";
+	runner.runWarningTest();
+}
+
 public static Class testClass() {
 	return CastTest.class;
 }

org.eclipse.jdt.core.tests.compiler/src/org/eclipse/jdt/core/tests/compiler/regression/GenericTypeTest.java

@@ -22763,19 +22763,7 @@ public void test0705() {
 }
 //https://bugs.eclipse.org/bugs/show_bug.cgi?id=97219
 public void test0706() {
-	String outputExpectedBelow17 = (this.complianceLevel == ClassFileConstants.JDK1_6)?
-			"----------\n" +
-			"1. WARNING in X.java (at line 9)\n" +
-			"	class BB extends AA<CC> { <U> BB test() {return null;} }\n" +
-			"	                                 ^^^^^^\n" +
-			"Name clash: The method test() of type BB has the same erasure as test() of type AA<T> but does not override it\n" +
-			"----------\n":
-				"----------\n" +
-				"1. ERROR in X.java (at line 9)\n" +
-				"	class BB extends AA<CC> { <U> BB test() {return null;} }\n" +
-				"	                                 ^^^^^^\n" +
-				"Name clash: The method test() of type BB has the same erasure as test() of type AA<T> but does not override it\n" +
-				"----------\n";
+	if (this.complianceLevel < ClassFileConstants.JDK1_7) return;
 	this.runNegativeTest(
 		new String[] {
 			"X.java",
@@ -22790,15 +22778,18 @@ public void test0706() {
 			"class BB extends AA<CC> { <U> BB test() {return null;} }\n" +
 			"class CC {}\n",
 		},
-		(this.complianceLevel < ClassFileConstants.JDK1_7)
-		? outputExpectedBelow17
-		: "----------\n" +
+		"----------\n" +
 		"1. ERROR in X.java (at line 4)\n" +
 		"	bb.<Object>test();\n" +
 		"	           ^^^^\n" +
 		"The method test() is ambiguous for the type BB\n" +
 		"----------\n" +
-		"2. ERROR in X.java (at line 9)\n" +
+		"2. WARNING in X.java (at line 5)\n" +
+		"	((AA<CC>) bb).test();\n" +
+		"	^^^^^^^^^^^^^\n" +
+		"Unnecessary cast from BB to AA<CC>\n" +
+		"----------\n" +
+		"3. ERROR in X.java (at line 9)\n" +
 		"	class BB extends AA<CC> { <U> BB test() {return null;} }\n" +
 		"	                                 ^^^^^^\n" +
 		"Name clash: The method test() of type BB has the same erasure as test() of type AA<T> but does not override it\n" +
@@ -29732,7 +29723,10 @@ public void test0899() {
 }
 //https://bugs.eclipse.org/bugs/show_bug.cgi?id=97693
 public void test0900() {
-	this.runNegativeTest(
+	Runner runner = new Runner();
+	runner.customOptions = getCompilerOptions();
+	runner.customOptions.put(CompilerOptions.OPTION_ReportUnnecessaryTypeCheck, CompilerOptions.IGNORE);
+	runner.testFiles =
 		new String[] {
 			"X.java", // =================
 			"public class X<R> {\n" +
@@ -29753,7 +29747,8 @@ public void test0900() {
 			"		Zork z;\n" +
 			"	}\n" +
 			"}\n",
-		},
+		};
+	runner.expectedCompilerLog =
 		"----------\n" +
 		"1. WARNING in X.java (at line 11)\n" +
 		"	((Comparable<R>) new Implements()).toString();\n" +
@@ -29769,7 +29764,8 @@ public void test0900() {
 		"	Zork z;\n" +
 		"	^^^^\n" +
 		"Zork cannot be resolved to a type\n" +
-		"----------\n");
+		"----------\n";
+	runner.runNegativeTest();
 }
 // Object array vs Object into generic method
 public void test0901() {

org.eclipse.jdt.core.tests.compiler/src/org/eclipse/jdt/core/tests/compiler/regression/MethodVerifyTest.java

@@ -3091,6 +3091,11 @@ public void test043c() { // ambiguous message sends because of substitution from
 			"	m.id(Integer.valueOf(111));\n" +
 			"	  ^^\n" +
 			"The method id(Integer) is ambiguous for the type M<Integer,Integer>\n" +
+			"----------\n" +
+			"2. WARNING in X.java (at line 5)\n" +
+			"	((E<Integer, Integer>) m).id(Integer.valueOf(111));\n" +
+			"	^^^^^^^^^^^^^^^^^^^^^^^^^\n" +
+			"Unnecessary cast from M<Integer,Integer> to E<Integer,Integer>\n" +
 			"----------\n"
 			// reference to id is ambiguous, both method id(A) in C<java.lang.Integer> and method id(B) in M<java.lang.Integer,java.lang.Integer> match
 		);